This invention relates to a printing head for use in an ink jet printer and a method for producing a printing head.
In conventionally known arrangements, a printing head for an ink jet printer employs piezoelectric elements as actuators. FIG. 14 is a fragmentary sectional view showing a construction of a conventional Kyser type printing head. A printing head 300 has on its surface a plurality of dot printing sections 305 arranged in an array extending at right angles to the section of FIG. 14, each dot printing section 305 comprising a front ink passage 301a, a pressure chamber 301b, a rear ink passage 301c, an ink nozzle 303a, an ink jet outlet 303b and a piezoelectric element 304.
The front ink passages 301a, pressure chambers 301b and rear ink passages 301c of the individual dot printing sections 305 are constructed by forming a specific pattern of recesses on a surface of a substrate 301 which is made of Photosensitive glass and then bonding a diaphragm 302 to the surface of the substrate 301 with an adhesive. Each piezoelectric element 304 serves as a pressure source for the front ink passage 301a. It is produced by forming electrodes 304a and 304b on opposite surfaces of a piezoelectric member 304c made of lead zirconate-titanate (hereinafter referred to as "PZT"), for instance. The individual piezoelectric elements 304 are bonded to the diaphragm 302 with an adhesive just at the positions of the pressure chambers 301b.
The ink nozzles 303a and ink jet outlets 303b of the individual dot printing sections 305 are made by bonding a nozzle plate 303, in which a pattern of the ink nozzles 303a and ink jet outlets 303b is preformed, to an end of the substrate 301, to which the diaphragm 302 is already attached, by use of an ultraviolet-curing adhesive.
The diaphragm 302 forms flexible walls of the pressure chambers 301b as well as walls of the front ink passages 301a and rear ink passages 301c.
The printing head 300 is produced in the following procedure. First, a surface of the substrate 301 made of photosensitive glass is subjected to a photolithographic process to form a recessed pattern of the front ink passages 301a, pressure chambers 301b and rear ink passages 301c. Then, the diaphragm 302 also made of photosensitive glass is bonded to the surface of the substrate 301 with the adhesive. The substrate 301 joined with the diaphragm 302 is hereinafter referred to as a "head assembly 306".
Next, a layer 307 of indium tin oxide (hereinafter referred to as "ITO") is formed as a common electrode on an outside surface of the diaphragm 302 of the head assembly 306. The piezoelectric elements 304 readily produced as discrete components are bonded to the diaphragm 302 just at the locations of the pressure chambers 301b with an epoxy adhesive. Then, the nozzle plate 303 having a water repellent finish on its ink streaming surfaces is bonded to the front end of the head assembly 306 with the aforementioned ultraviolet-curing adhesive to complete the printing head 300.
To produce elongate printing heads for constructing a line head suitable for standard A4-size paper, for instance, there should typically be 5100 dot printing sections available. For this, it is essential to develop a technique to arrange a large number of dot printing sections on a line head structure at high density and high accuracy. In particular, individual piezoelectric members which will serve as pressure sources must be small-sized and yet provide great electrostriction. Furthermore, they must be attached in exact locations of individual pressure chambers.
The above-mentioned conventional printing head 300 is produced by individually bonding the piezoelectric elements 304 prepared as discrete components to the diaphragm 302 at the locations of the pressure chambers 301b with the epoxy adhesive. This producing method is complicated and it is difficult to align the individual piezoelectric elements 304 with high positioning accuracy.
Although bimorph cells are known to provide higher electrostriction, it is difficult to use them as piezoelectric members in producing a line head of conventional type as a small-sized structure is essential.